This invention relates to nuclear reactors and, in particular, to a method and apparatus for determining if a nuclear reactor fuel rod is leaking.
One problem faced in the utilization of nuclear power as an energy source is the radioactive contamination of the reactor facility. One source of such contamination is leakage of fission product gases and other radioactive materials from a fuel element during reactor operation. These contaminants then enter the coolant material and are carried to other areas in the reactor facility. When such contamination occurs, it is necessary that nuclear fuel bundles which have prematurely failed be removed from the reactor core and replaced with fresh fuel. The replacement process, normally accomplished during scheduled plant outages, involves two steps. First, fuel bundles suspected of containing defective fuel pins are identified, then they are removed and replaced with good fuel bundles. After removal, suspect bundles may be disassembled, the defective fuel rods segregated by nondestructive examination, and then reassembled with good fuel rods.
With present practice, identification of faulty fuel, either in-core or after bundle disassembly, is a time-consuming process which contributes substantially to the overall cost of reconstituting the fuel load.
Attempts have been made to reduce and overcome the disadvantages of the standard practice by devising various methods for rapidly testing the fuel rods for leakage without having to remove them from the reactor core; see U.S. Pat. Nos. 3,296,864, 3,230,771 and 3,350,271. These methods have not been successful because the methods could not accurately determine the leakage or the apparatus could not function in the reactor environment.
In copending application, Ser. No. 200,698, filed Nov. 22, 1971, now U.S. Pat. No. 3,823,068, a method to detect fuel pin leakage without removing the fuel elements from the reactor is disclosed wherein the fission gas pressure activates a flexible diaphragm or bellows assembly to produce measurable fluctuations in an eddy current established about the fuel rod upper end cap.
In copending application, Ser. No. 422,383, filed Dec. 6, 1973, another method and apparatus for facilitating the detection of fuel pin leakage and reducing downtime for nuclear reactors is disclosed. The instant invention comprises a probe for use with the apparatus of the copending application.